Fluorine occurs in nature in various minerals and industrially fluorine is obtained from the mineral fluorspar, CaF.sub.2. Finely ground fluorspar is reacted with concentrated sulfuric acid to yield hydrogen fluoride. This is dried and then reacted with potassium fluoride to form potassium hydrogen fluoride, KF.nHF, where n has a value from 1 to 3. Anhydrous potassium hydrogen fluoride is subjected to electrolysis and fluorine gas is obtained at the anode. At present fluorine is an expensive chemical, particularly when purchased in small quantities. The market for fluorine is large and growing. Fluorine is used, for instance, in the nuclear industry for the manufacture of UF.sub.6, and SF.sub.6 is now being used as a dielectric in transformers, in place of chlorinated biphenyls.
Magnesium fluoride does not appear in nature, but large quantities of fluorine are present in uranium-contaminated magnesium fluoride that is obtained from reduction of UF.sub.4 to uranium metal by the thermite reaction. At present this uranium-contaminated magnesium fluoride is stockpiled, at considerable expense.
Another source of fluorine is UF.sub.6, particularly tails from a uranium-enrichment process in the nuclear industry. Naturally occurring uranium is composed mostly of .sup.238 U, with about 0.71 % of the radioactive isotope .sup.235 U. For use in the nuclear industry the content of radioactive .sup.235 U must be increased to give enriched uranium. Enrichment is achieved for instance by gaseous diffusion of UF.sub.6. In addition to the desired enriched product, the enrichment process yields a large quantity of UF.sub.6 that is depleted in content of .sup.235 U. An economical process for converting the depleted UF.sub.6 into uranium metal and fluorine would be of considerable value. The fluorine could be recycled to the formation of undepleted UF.sub.6 for subjection to the enrichment process. The depleted uranium metal has uses, for instance, in shielding reactors and in military armour and projectiles.
A letter to the editors of the Journal of Nuclear Materials 149 (1987) 103-107 discloses that a small amount of uranium metal has been obtained by subjecting UO.sub.3 or UF.sub.6 to the effect of an argon plasma.